Organomodified silicones have been produced by conventionally known reaction schemes in accordance with the types of organic groups introduced into the silicone. Since there are typically few cases in which the reaction for introducing organic groups progresses at a chemical equivalent (molar equivalent) level, the introduction reaction is ordinarily completed by using an excessive amount of an organic modifier. Accordingly, the unreacted organic modifier is present in the reaction system in addition to the organomodified silicone serving as a product.
When the organic modifier is a compound with a relatively low boiling point such as an α-olefin having at most 12 carbon atoms, the residual compound (impurities) can be reduced by stripping treatment, whereby the reaction mixture is heated so as to establish a decompressed state. However, when the boiling point of the organic modifier is high, or when the organic modifier is a polymer compound, purification by means of stripping is not effective, so it has been difficult to obtain a high-purity organomodified silicone on a commercial scale. This is due to not only the fact that stripping at an excessively high temperature causes the degeneration of the product or undesirable side reactions, but also the fact that a technique of stripping impurities having a high boiling point at an even higher temperature is inefficient in an actual production process.
Another technique for increasing the purity of an organomodified silicone containing a residual organic modifier is an extraction (or precipitation/re-precipitation) separation method utilizing the difference in solubility between impurities and the main component. For example, when the organic modifier is a hydrophilic compound, in an extraction separation method, most impurities are first extracted and removed with a hydrophilic solvent (alternatively, the main component is conversely extracted with a lipophilic solvent). However, phase separation in the extraction process ordinarily takes time, and this does not yield clean separation. This results in an increase in waste and a decrease in yield and productivity. In addition, depending on the structure of the organomodified silicone, there are many cases in which the entire system enters an emulsified state and cannot be separated, which leads to poor versatility.
On the other hand, a precipitation and re-precipitation method is a technique of dissolving an organomodified silicone containing a residual organic modifier in an organic solvent with solubility in both the impurities and the main component, and precipitating and separating the main component by gradually adding water, for example. Patent Document 1 discloses a high-purity polypropylene glycol-modified organosiloxane polymer obtained by a precipitation and re-precipitation method. However, the total amounts of the organic solvent and water that are used in this method are ten times the amount of the organomodified silicone each time re-precipitation is performed, and this is repeated three times to obtain a high-purity organomodified silicone with no impurities. Accordingly, taking into consideration problems such as the low productivity in relation to the number of reactions and the large amount of waste water treatment, application to mass production on a commercial scale is difficult. In addition, when the organic modifier is a polyethylene glycol (PEG) type modifier, the hydrophilicity and surface activity performance of the corresponding organomodified silicone are increased, so separation and purification are often difficult with this method.
Patent Document 2 discloses an organopolysiloxane derivative having a sugar residue but not containing an unreacted starting material, which is obtained by a membrane separation method using a dialysis tube. However, a dialysis time of three days is required to obtain 10 g of a high-purity organomodified silicone, so this method cannot be considered suitable for mass production on a commercial scale from the perspective of efficiency. In addition, in Patent Document 2, it is stated that the purification of the organopolysiloxane derivative is also possible by column chromatography. Further, Patent Document 3 discloses a glyceryl ether-modified silicone purified by a silica gel column. However, column chromatography requires the circulation of a large amount of a solvent in order to obtain a high-purity organomodified silicone, and there are many problems with production on a commercial scale, such as the apparatus design, the recovery of the waste solvent, the removal of the solvent from the recovered solution, and low productivity.
Another example of a technique for increasing the purity of an organomodified silicone containing a residual organic modifier is an attempt to improve the transparency of a product by repeating precision filtration or adsorption agent treatment so as to reduce the amount of the residual organic modifier, which is also a cause of turbidity or phase separation. However, this residual organic modifier is ordinarily a liquid in the temperature range in which the organomodified silicone serving as the main component is in the liquid phase, so a technique of solid/liquid separation utilizing a filter aid, a cartridge filter, or the like is not only irrational, but is also mostly ineffective in actuality.
Patent Document 4 discloses a purification method for an alkyl glyceryl polysiloxane derivative by means of ultrafiltration utilizing a diafiltration method. However, since the pore diameter of an ultrafiltration membrane is small and the film tends to become obstructed in a short amount of time, ultrafiltration must be performed after diluting an organomodified silicone containing an organic modifier around ten times with a volatile solvent such as hexane. Therefore, there are problems such as the removal of the solvent from the filtrate, low productivity, and operator safety.
In addition, the techniques of Patent Documents 5 to 12 are known as purification methods for polyether-modified silicone compositions. Polyether-modified silicones are typically produced by performing an addition reaction on an organohydrogensiloxane and a polyoxyalkylene having a terminal double bond in the presence of a precious metal catalyst such as chloroplatinic acid. Patent Documents 5 to 12 disclose deodorization techniques of stabilizing the unsaturated group portion of excess polyether (residual organic modifier), which is a cause of the odorization of the polyether-modified silicone composition, by means of hydrolysis or hydrogenation treatment, and it is not the case that a high-purity polyether-modified silicone is obtained. In these techniques, the excess polyether changes the structure thereof and continues to remain in the composition.
On the other hand, there have also been reported attempts to produce a high-purity polyether-modified silicone from the synthesis stage rather than purifying a polyether-modified silicone composition by means of after-treatment. A representative technique is one in which an organic modifier with a structure that is unlikely to cause isomerization, such as γ,γ-dimethylallyl etherified polyoxyalkylene, is used as a polyether starting material instead of a conventional allyl etherified polyoxyalkylene (Patent Documents 13 to 16). However, the unsaturated alcohol used as an initiator in order to obtain this polyether starting material is not a substance that can be obtained easily, so this is not a method with which the polyether-modified silicone can be mass-produced inexpensively. In addition, this unsaturated alcohol serving as an initiator is a tertiary alcohol, and the addition reactivity of alkylene oxide to this alcohol is much worse than when a conventional allyl alcohol (primary alcohol) is used. Therefore, with an ordinary catalyst, there are problems such as residual initiator alcohol with low reactivity, difficulty in obtaining a polyether starting material with the desired degree of polymerization, and a broad molecular weight distribution. In addition, ether bonds adjacent to quaternary carbons of γ,γ-dimethylallyl etherified polyoxyalkylene are unstable and are susceptible to hydrolysis, so at the time of the production of a polyether-modified silicone, it is necessary to use a slightly excessive amount of organohydrogensiloxane and to be careful that the entire amount of the polyoxyalkylene is consumed and not left behind. If left behind in even a slight amount, there is a risk that a strong odor will be generated due to degradation products of low molecular weight after the polyether-modified silicone is blended into a cosmetic or the like, so it is difficult to stabilized production activities or quality from the perspective of the formulation design or confirmation operation for complete consumption.
In addition, similar techniques have been reported in which a long-chain alkenyl etherified polyoxyalkylene (Patent Document 17) or a vinyl etherified polyoxyalkylene (Patent Document 18) is used instead of a conventional allyl etherified polyoxyalkylene. However, a long-chain alkenyl etherified polyoxyalkylene is isomerized during a hydrosilylation reaction, so approximately 10 wt. % remains in the reaction product. Therefore, a high-purity polyether-modified silicone cannot be obtained with the technique of Patent Document 17. On the other hand, although a vinyl etherified polyoxyalkylene is unlikely to cause isomerization, according to Patent Document 18, when Si—H groups and vinyl groups are reacted so as to be equimolar, the reaction is not completed, and Si—H groups remain in an amount of from 5 to 80 ppm. This means that unreacted vinyl etherified polyoxyalkylene is left behind, so a high-purity polyether-modified silicone cannot be obtained with this method either. In addition, vinyl ether-type compounds always have various problems in that the vinyl groups tend to react with hydroxyl groups in the reaction mixture and form acetal, which makes the compound susceptible to vinyl-type polymerization.
Another technique attempting to produce a high-purity polyether-modified silicone from the synthesis stage is reported in Patent Document 19. This consists of a process of performing a hydrosilylation reaction on an alcohol compound containing carbon-carbon double bonds with a relatively low molecular weight and an organohydrogensiloxane, removing the unreacted starting material or the like by stripping so as to obtain a high-purity alcohol-modified polysiloxane, and then addition-polymerizing alkylene oxide with this product. However, in this method, Lewis acid is used a catalyst for addition polymerization, so the coloration of the resulting polyether-modified silicone is strong, and it is also difficult to remove the catalyst. In addition, cyclic polyether impurities resulting from the homopolymerization of alkylene oxide are likely to be produced, and it is difficult to obtain a high-purity polyether-modified silicone with good reproducibility. Further, the process is too complex and unrealistic for silicone producers.
As described above, when the boiling point of the organic modifier is high or when the organic modifier is a polymer compound, there have been practically no known useful methods for stably producing a high-purity organomodified silicone on a commercial scale. Further, there has also been no known technique of increasing the purity of an organomodified silicone which can be applied regardless of the type of organic modifier and can reasonably accommodate production on a commercial scale.
On the other hand, organomodified silanes are typically sold after the purity is increased by distillation purification, even in industrial production, due to the property of being low-molecular compounds having a boiling point. In the production of organomodified silanes, the purity is wholly increased by distillation after being partially purified by extraction or the like following a synthesis reaction due to the fact that plants are already provided with precision distillation equipment and the fact that they are monomolecular so, in contrast to organomodified silicones, problems such as sub-reactions or gelification are unlikely to occur even when distillation is performed at a high temperature. That is, organomodified silanes often have a high boiling point, and the production process causes increases in energy cost when performed at a high temperature for a long period of time, but it is accepted that this is inevitably translated into the sales price. Therefore, there has been practically no search for techniques for increasing purity as an alternative to distillation.
In particular, when the organic modifier of an organomodified silane is a polymer compound such as a polyether or a compound with a high boiling point so that distillation is difficult, purification by distillation is not possible, so it has been difficult to obtain high-purity organomodified silanes.